You are looking for what family? Those earlier in the ancestral line(s) or those who are descendants?
Searching for ANY information will be pointless without knowing WHEN Severin was born and when "Roy Larsen" was born. See the link at the bottom of this posting.
The 1900 US census shows a Severin Olsen in Boston, MA married to a woman named Lena. He is listed as born in July 1871 in Norway and immigrated to the US in 1892. Study that census to find if that is the man you are seeking.https://familysearch.org/pal:/MM9.1.1/M9YV-LMP
IF you find that is the right man - then FamilySearch.org also has a record of his marriage to Lena in Boston which gives his parents names - vital to a search for a name which would be fairly common in Norway!https://familysearch.org/pal:/MM9.1.1/FHFM-QZD
With those parents names on top of the info about when born found in those two earlier links FamilySearch.org can be used again and -https://familysearch.org/pal:/MM9.1.1/NWZ9-S5Hhttp://www.rootsweb.ancestry.com/~wgnorway/good-queries.htm